1. Field of the Invention
The present invention relates to a dispensing apparatus for paste or other types of adhesive agents, etc.
2. Prior Art
In die bonding apparatuses, for example, a fixed amount of bonding materials such as paste is dispensed onto a lead frame circuit board, etc., and the die is bonded on top of the dispensed paste. The paste is dispensed by supplying air under positive pressure to a syringe filled with paste.
Conventionally, the supply of air to the syringe is controlled by opening a dispensing electromagnetic valve, which is provided between the syringe and the positive-pressure air supply source, for a preset period of time. However, since the dispensing electromagnetic valve is controlled for a preset time period, several problems arise.
First, when a given air pressure is applied to the syringe for a fixed period of time, the amount of paste dispensed varies in accordance with the amount of paste remaining in the syringe. If the paste is opaque or if the paste is transparent and the syringe is opaque, the operator has no way of directly knowing the amount of paste remaining inside the syringe. In such cases, the amount of paste remaining in the syringe is ascertained indirectly from the amount of paste squeezed out from the side surfaces of the die by the die bonding operation after the paste has been dispensed onto the lead frame, etc. With such an ascertained value, the operator resets the time and air pressure.
Another problem arises in that since the paste and syringe are usually opaque, and the operator does not know the amount of paste remaining in the syringe. Furthermore, since the die bonding apparatus is automated and it runs without the presence of an operator, the apparatus may inadvertently run with no paste in the syringe, resulting in improper paste dispensing (no paste being dispensed) which leads to improper die bonding in the subsequent die bonding process. In addition, small amounts of paste may drip from the tip of the syringe when the apparatus is stopped.